The invention relates to an endoprosthesis for a knee joint, including a femoral and a tibial component between which a slide bearing is disposed which comprises a femoral and a tibial bearing half.
The prior art endoprostheses have only one degree of freedom: they can be flexed or extended in only one plane.
Additionally, first models of rotary prostheses have become known which are capable of providing to a certain extent rotation of the lower leg with respect to the thigh as it is possible with a natural knee joint. However, such rotation is imparted undamped to the anchors with which the bearing halves are fastened to the bone. The rotary moment effecting the rotation is thus transmitted to the anchors by a hard jolt. Such impact stresses involve the danger of loosening the anchors to the bone.
The same danger is present if the knee joint prosthesis is bent to such a degree that parts of the tibial component abut on the femoral component. This also generates impact stresses which may loosen the anchors of the components in their associated bones.